The aged are more susceptible to accidental hypothermia and heatstroke than any other population and there is evidence that changes in sensitivity of the central temperature controls may be responsible for, or contribute to, dysthermia in aged homeotherms. The broad aim of the proposed project is to learn how the central temperature control mechanism of the aged primate differs from that of younger animals in its response to: 1) drugs widely prescribed for the elderly which are known or suspected to affect body temperature; and 2) neurotransmitters that are believed to be components of central thermoregulatory pathways. Central transport mechanisms protect the brain from prolonged and deleterious stimulation by drugs and endogenous substances. There is little information as to whether or how these transport processes are different in the brain of the aged primate. One aim of these projects is to learn whether inhibition of facilitated transport processes differentially affects the response of central temperature controls of aged homeotherms to drugs and neurotransmitters. Subtle differences in central transport processes of aged homeotherms might lead to imbalance of thermoregulatory controls and increase the possibility of dysthermia. Information obtained in these experiments will further our understanding of how aging affects a central homeostatic control that is essential to life and normal existence of homeotherms.